1. Statement of the Technical Field
The inventive arrangements relate to user control knobs which are mounted on rotatable control shafts, and more particularly to methods and systems for retaining user control knobs in position on rotatable control shafts.
2. Description of the Related Art
Many devices, including electronic devices, utilize manually operated rotatable control elements. These control elements include a shaft which rotates for purposes of actuating an electronic or manual control. Conventional shafts have a D-shaped cross-sectional profile. The D-shaped cross-sectional profile includes a planar face on a portion of the shaft which facilitates indexing of the knob in the proper orientation on the shaft. The D-shaped profile is also useful because it prevents rotation of knob relative to the shaft. A retention system is often provided to secure the knob on the shaft. A common retention system comprises a set screw threaded into the knob. The set screw engages the shaft to prevent the knob from sliding off the shaft.
Knob retention systems that use set screws can, under certain circumstances, permit control knobs to slide off the shaft and become lost. Most often, such loss occurs when the set screws become loose and/or the electronic device is accidentally dropped. These kinds of failures are undesirable, especially for equipment used by first responders or military operators. In order to overcome these limitations, designers have developed alternative knob retention solutions. For example, one such solution uses specialized knob inserts and customized control shafts in which special grooves have been provided. The insert is designed to snap into the groove. The control is then secured into the housing of the electronic device. Finally, a knob is snapped onto the insert.
Existing solutions which overcome the set-screw problem are not entirely satisfactory. The required customization of control shafts generally tends to increase component costs since these custom features are not normally included in commercial control shafts. Another problem with existing solutions is that the normal axial play which is present in rotatable controls tends to inhibit proper assembly of knobs onto the inserts. In other words, the shafts tend to rotate as the insert is being snapped into the specialized grooves formed on the shafts. When the knob must be removed from the electronic device, the shafts are sometimes damaged or can be pulled out of the control, due to the axial forces which must be applied during knob removal. Also, knob inserts sometimes become lodged within the knobs, and damage can occur to such inserts during knob removal.